1. Field of the Invention
The present invention relates to an optical fiber and an optical fiber ribbon.
2. Description of the Related Art
Schemes used for signal transmission inside an apparatus can be two types: electric transmission scheme and optical interconnection scheme. With the recent increase of the speed of CPU clock frequencies, occurrence of cross-talk, which is caused by high density wiring, is a problem for the electric transmission scheme. Therefore, application of a waveform shaping technique, etc., is necessary. As a result, when the electric scheme is employed as the signal transmission scheme in an apparatus, it is known that a transmission distance of about 100 m and a transmission speed of about 10 Gbps are the limits for the transmission. On the other hand, the optical interconnection scheme enables execution of transmission over a much broader band compared to the electric transmission scheme and also enables configuration of a signal transmission system that uses small-size low-power-consumption optical components. Therefore, the optical interconnection scheme is drawing attention as an in-apparatus signal transmission technique that is to replace the electric transmission scheme.
The optical interconnection scheme includes a scheme that uses optical waveguide circuits as an optical transmission unit and a scheme that uses optical fibers. Because it is desirable that all optical components used in an apparatus can be accommodated saving as much space as possible, an optical fiber that enables flexible wiring and that enables small-loss optical transmission is positioned as one of the optical components that are suitable for the optical interconnection.
Conventionally, a multi-mode optical fiber (MMF) has been used as an optical fiber for short-distance optical transmission. Normally, an MMF has a core diameter that is 10 times as large as that of a single-mode fiber (SMF), so that the MMF needs no high precision for connection between the optical fiber and a light source because of the magnitude of the numerical aperture thereof. Therefore, the MMF enables easy connection. Especially, an approach is often used that employs a Vertical-Cavity Surface-Emitting Laser, hereinafter, “VCSEL” of an oscillation wavelength of 850 nm as a light source and employs a graded-index optical fiber that is a type of multi-mode optical fiber as an optical transmission medium. A graded-index optical fiber is an optical fiber that suppresses the influence of mode dispersion by optimizing the refractive index profile shape in a core region. A graded-index optical fiber of which the refractive index profile shape is precisely controlled enables high-speed optical communication at a transmission speed of 10 Gbps and connecting a distance of about 100 m. However, aiming at performing longer-distance transmission or higher-speed transmission, consideration of application of a SMF which generally has wider bandwidth is being started. Recently, research of a GaInAs/GaAs-based semiconductor laser as a light source applied in such a case is being proceeded. This laser is characterized in that the laser has an oscillation wavelength of 1,100 nm to 1,200 nm, has a low oscillation threshold value, has an excellent temperature property, and may directly modulate at 10 Gbps, etc. Therefore, the laser is drawing attention as a light source to be used in a LAN, etc. The oscillation wavelength thereof can be varied and research and development thereof for both of 1,100 nm and 1,200 nm have been carried out so far and presentations in academic societies thereon are performed. For example, Non-Patent Document 1 and Non-Patent Document 2 disclose that transmission is executed through an SMF using a GaInAs/GaAs quantum well laser as a light source. When an SMF is used, high-speed optical communication at a transmission speed of about 40 Gbps is enabled.
Non-Patent Document 1: F. Koyama et al., “1.2 μm highly strained GaInAs/GaAs quantum well laser for singlemode fibre datalink”, ELECTRONICS LETTERS, Vol. 35, No. 13, pp. 1079-1081, June, 1999.
Non Patent Document 2: F Koyama et al., “Data Transmission Over Single-Mode Fiber by Using 1.2-μm Uncooled GaInAs/GaAs Laser for Gb/s Local Area Network”, PHOTONICS TECHNOLOGY LETTERS, Vol. 12, No. 2, pp. 125-127, February, 2000.
As above, a demand exists for realization of an optical fiber of which the bending loss and the connection loss are both reduced, that enables high-speed optical transmission, and that is suitable for easily constructing an optical interconnection system. A demand also exists for realization of an optical fiber that can be run at a small bending radius, of which the break probability due to bending is small, and of which extra length can be accommodated.